The present invention relates to a device for ascertaining the condition of at least one wiper blade of a motor vehicle.
For safety reasons, motor-vehicle wiper blades must be cleaned or replaced regularly. Dirty wiper blades lead to inadequate wiping results, so that visibility is affected. The same holds true for rubber wiper elements (otherwise referred to as "blade rubbers") which have worn out or have become too old. Different influence variables have an affect on the wiping result and limit the service life of wiper blades, it thus being very difficult for the motor-vehicle driver to determine with sufficient accuracy the point of time to change the wiper blade.
German Published Patent Application No. 36 39 831 describes a known device according to which the condition of a wiper blade is determined. In doing this, the wear and tear of a wiper strip is monitored by an optical moisture sensor, with which the windshield to be cleaned is scanned before and after a wiping operation. With these means, the quality of the wiping field is objectively judged, and information is obtained about the wear and tear of the viper strip. This moisture sensor is accommodated in a scanning device, preferably similar to a plotter, by which the windshield to be cleaned is scanned in the individual areas. Thus, this corresponds to a mobile test apparatus, and is used merely to detect the condition of a wiper blade.
The device of the present invention for ascertaining the condition of at least one wiper blade of a motor vehicle provides for using a rain sensor which is already at hand for determining the time to replace the wiper blade or to clean it. Therefore, a component, namely the rain sensor, is not only used normally for detecting a rain event and thus for controlling the windshield wiper delay control, but according to the present invention, is used for ascertaining the condition of the wiper blades. Thus, in the present invention, the rain sensor is given a double function. For example, the rain sensor is located in the area of the rear-view mirror at the windshield, and there detects the state of the window surface with respect to precipitation. According to the present invention, the rain sensor is also able to detect the condition of the windshield with respect to possible dirt, deposits, etc., whereby a conclusion is possible about the condition of the wiper blade, namely concerning its dirtiness, or concerning the wear or ageing of the wiper blades, that is to say, of the rubber wiper elements.
As already mentioned, the rain sensor is preferably arranged at the vehicle window having the wiper blade.
According to a further development of the present invention, the rain sensor is arranged within the area of the vehicle window swept over by the wiper blade. This ensures that the rain sensor can directly detect the wiping result of the wiper blade.
It is advantageous if the device has an evaluation circuit which evaluates the data from the rain sensor. This evaluation circuit is used to evaluate the data coming from the rain sensor as to the condition of the wiper blade, and to trigger an appropriate reaction when certain limiting values are exceeded. Preferably, the evaluation circuit carries out a statistical evaluation of the data supplied by the rain sensor.
The evaluation by the evaluation circuit is carried out in particular with regard to dirtiness of the wiper blade and/or dirtiness of the rain sensor, and/or wear and tear or over-ageing of the rubber wiper element. To this end, it is determined whether the acquired data changes slowly and continuously, which indicates wear of the rubber wiper element. If the data changes relatively quickly and continually, the wiper blade is dirty. If certain data are ascertained which do not correspond to a perfect condition of the system, this suggests that the rain sensor is dirty, this ascertained dirtiness being constant in most cases, thus scarcely subject to a change. By appropriate evaluation, particularly along statistical lines, the individual conditions of the wiper blade can be ascertained with sufficient accuracy.
Preferably, a signal is emitted when a specific characteristic condition of the rubber wiper element has been detected. For example, the signal can be effected optically and/or acoustically; in particular, it is advantageous to provide a display which, by variable activation, e.g. blinking or sustained light, calls upon the driver to change the wiper blade, or to clean the rain sensor and/or the rubber wiper element.